Efficiently selecting a relevant subset of sensory information for further processing is a fundamental mechanism that is central to a whole host of cognitive functions. This process of perceptual selectivity, also referred to as 'attention', plays a key role in determining what we perceive. A large body of evidence, acquired over the last 5 years from neurophysiology, functional imaging and behavioral investigations, has allowed researchers novel insights into the psychological and neural mechanisms mediating attentional selection. Although we currently have at our disposal the unprecedented means for elucidating brain-behavior correspondences in the domain of visual attention, far more questions and contradictions have emerged than have answers. A greater degree of specificity and fine-grained analysis at both the behavioral and the brain level is now required to advance further our understanding of visual attention, specifically, and visual cognition, more generally. The specific aims of the current project include (1) evaluate the consequences that interhemispheric attentional imbalance has on sensory signals elicited in early and late visual cortices of the two hemispheres;and (2) investigate the psychological and neural consequences of a rehabilitation procedure aimed at recovery from this hemispheric imbalance. The results of this project will significantly advance our understanding of how attention influences perception in the normal functioning neural system and in patients with visuo-spatial neglect (a neurological disorder). Gaining a more fine-grained understanding of attentional selection is ever more important given that various types of psychiatric as well as neurological disorders co-occur with attentional dysfunction (ADHD, schizophrenia, Balint's syndrome, visuo- spatial neglect, autism) and affect many individuals - male and females of all age groups, socioeconomic strata and ethnicities. In summary, the results from this project may have broad application by providing further understanding into the neural mechanism of attentional selectivity as well as by fostering insights into possible neuro-rehabilitative techniques that might be used to ameliorate the behavioral deficits associated with attentional disorders. PUBLIC HEALTH RELEVANCE: Characterizing the effect and impact of attention on sensory responses promises to improve significantly our understanding of neural, and some psychiatric, disorders that affect attention orienting (such as hemispatial neglect, Balint's syndrome, attention deficit hyperactivity disorder, schizophrenia, and autism). Here, we investigate hemispatial neglect, a neurological deficit most commonly present after stroke, a condition that affects at least 500,000 Americans every year (according to the American Heart Association). A major contribution from this study will be both an enhanced understanding of attentional dysfunction in hemispatial neglect, and also a clear mechanistic explanation of the effects of a neuro-rehabilitative tool that may be used to aid the recovery from a debilitating neurological disorder.